Hot Rod Forum banner

1 - 12 of 12 Posts

·
Registered
Joined
·
43 Posts
Discussion Starter #1
Just replaced the top end on a 305 with stock cast heads and an aluminum intake, Everything works fine run it around town for a few days it is all good. Take it out on the hiway and run it a little hard and I get a vacuum leak. This is the second intake and have tried gaskets from Mr. Gasket and Fel-Pro. New PCV valve and two breathers on the valve covers passenger side all new. I need help, getting real good at installing an intake but didn't want to.
 

·
Registered
Joined
·
1,384 Posts
How can you tell you have a vacuum leak on the highway, like what symptoms?


Also, Fel Pro makes an extra thick (almost 1/8") gasket for BBC's. Don't know if they make one for yours?
 

·
Registered
Joined
·
5,733 Posts
sealing engines leaks

An old neighbor used to build circle track cars, He would hook up a long vacuum hose from his ranchero to the dipstick tube on his new engines on the stand . then use a stethoscope to listen for leaks. He would then use some gasket sealer and the vacuum would suck in the sealer and stop the leaks.
 

·
Registered
Joined
·
43 Posts
Discussion Starter #4
Intake vacuum leak

55 Tony I don't know about the vacuum leak on the hiway it is after running it hard that the leak starts like on the hiway, It happens after running at about 5-6000 RPMs for a minute or less.

 

·
Registered
Joined
·
1,384 Posts
An old neighbor used to build circle track cars, He would hook up a long vacuum hose from his ranchero to the dipstick tube on his new engines on the stand . then use a stethoscope to listen for leaks. He would then use some gasket sealer and the vacuum would suck in the sealer and stop the leaks.
That sounds good, but when I had leaks they were always going to the crankcase.
 

·
Registered
Joined
·
43 Posts
Discussion Starter #7
Timothale,

That sounds like a great idea a buddy has a vacuum pump for AC that should work even better. Problem is I don't know what to do about it happening again. The gaskets seal good and everything like I said it only leaks after running at high RPM for a little bit.
 

·
Registered
Joined
·
3,867 Posts
I don't know if you re torque you intake or not after a few heat cycles but i always do as my new build I did back in the spring after a few heat cycles I went to re torque and some of the bolts were loose more then i was expecting and nothing bad or to worry about but loose enough that it was off about 5 ftlbs or so. I always torque mine at 25 ftlbs. I would also try and have the engine running and I use a propane torch unlit of course and let it spray around the intake if I ever looked for vacuum leaks or spray with carb cleaner and see if the idle would change.

The best thing is if you have a smoke machine and look for any smoke being sucked in around the intake flange.
 

·
Registered
Joined
·
5,435 Posts
55 Tony I don't know about the vacuum leak on the hiway it is after running it hard that the leak starts like on the hiway, It happens after running at about 5-6000 RPMs for a minute or less.

That would be a strange vacuum leak.
In those running conditions your vacuum should be close to zero.
Do you hear something or see something?
 

·
Music and Hot Rods
Joined
·
1,725 Posts
Use a straight edge on the intake gasket surfaces and check for warpage. My guess is that the intake it out more than .010"
 
1 - 12 of 12 Posts
Top